Plant Nutrient Deficiencv Symptoms J
PHYSIOLOGICAL BASIS E. E. DETURK University of Illinois, Urbana, Ill.
A fairly large and apparently increasing
plants to adapt themselves to varied soil environments. In spite of this adaptability, symptomatic indications of maladjustments in crop plants have become increasingly prevalent in recent years. Biochemical studies of normal and affected plants, considered in connection with growth and yield response to soil treatment, have contributed to an understanding of the relation between plant symptoms and the disturbances in plant metabolism brought about by malnutrition. The results lead to more accurate diagnosis of plant malnutrition by aid of symptoms.
number of chemical elements is coming to be recognized as necessary, or in some cases beneficial if not essential to the normal growth and reproduction of higher plants. The quantitative requirements of the respective elements vary from minute traces to comparatively large amounts, and the concentrations tolerated by plants are limited to a narrow range with some elements but extend over wide ranges with others. The toleration of n wide range of concentrations of the major nutrient elements is an important factor enabling
A
GROWING plant is a remarkable organism, not only in
and the converse may be true. Plants may suffer hunger as a result of various causes, among which are (a) insufficient supply in the soil, (b) too low a degree or rate of solubility, (c) physiological unavailability-i. e. inhibition of absorption by other ions or by unfavorable hydrogen-ion concentrationand ( d ) physiological unavailability within the plant-i. e., inability of the plant to utilize an element after absorption. Although rnany symptoms have come to be recognized as indicative of specific deficiencies, biochemical studies have shown that the connection between the symptom and its cause is usually indirect-namely, a disruption of the normal balance of a series of interdependent physiological processesand this maladjustment often consists in the relative rapidity a t which the various processes take place. The fundamentally basic element of all living substance is carbon, and the conversion of carbon from carbon dioxide to carbohydrates by photosynthesis is the starting point of all plant syntheses. The sugars produced by photosynthesis may then be considered a semiraw material in the production of other compounds. Proteins are the chief nitrogenous constituents in the protoplasm of living cells, while phosphorus compounds are important both in nuclear and cj~toplasmicmaterials and activities-in fact, wherever metabolic activity is in progress. As a consequence, the functions of these three groups of substances-nitrogen compounds, phosphorus compounds, and carbohydrates-are so closely interrelated in plant growth that many malnutrition symptoms are found to be associated with disturbances in some part of this three-cornered system. These relations can be illustrated by the examples which follow.
the great number of highly complex organic substances which make up its living substance and supporting framework, and in the complexity and nicety of balance of the interrelated reactions which take place in its growth, but also in the fact that as a manufacturing concern it must operate at full speed throughout the time i t is under construction. Proteins and oils, phosphatides, nucleic acids, carbohydrates, and many other compounds are composed of comparatively few elements which enter the plant as simple compounds or ions: Con, HzO, PO1---, Koa-, Ca++, K+, etc. The number of necessary elements exceeds the number that becomes a part of the living tissues, and the number found in plants goes beyond those now known to be necessary. Just how many of the chemical elements are essential to growing plants is not known. The classic family of ten has gradually enlarged to take in manganese, boron, zinc, and copper, and still others will probably be added. All these elements are often classified into major and minor, depending chiefly on the quantities required by crop plants. The toleration of fairly vide variations in concentration of the major elements is a n important factor in the adaptability of plants to widely different soil conditions. I n spite of this tolerance, external symptoms of maladjustments in crop plants havc become increasingly prevalent in recent years. The symptoms are frequently traceable to deficiencies in the soil supply of one or more elements. But this is not always the case. Excessive concentrations may be equally harmful. Indeed the deficiency of one element may be considered as an excess of some or all of the others, 648
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When the essential elements are all supplied in satisfactory proportions, but at too slow a rate, the usual result is a low plane of metabolism-slow growth, small plants a t maturity, low seed yield in proportion to straw in seed plants-but no specific symptoms observable in the plants themselves.
Nitrogen Deficiency When nitrogen becomes deficient, the first result is a slowing down of the growth rate, but this is not peculiar to nitrogen deficiency alone and cannot be taken as a symptom. The plants tend to be slender, to branch or tiller less than normally, and to suffer a decrease in green color. The last may be a paling of the green or, more frequently, the appearance of yellow coloration in the leaf blades followed by necrosis of the tissues. I n addition to chlorophyll, green leaves contain the yellow pigments carotene and xanthophyll, and they may also contain flavones (another group of pigments, chiefly yellow). These pigments, normally masked by the chlorophyll, become visible on its disappearance. The chlorosis, followed a few days later by death of the tissues, proceeds from tip to base of the leaf, first along the midrib in corn and other grasses and then up the plant from older to younger leaves. This symptom, commonly known as firing, may not be distinguishable from that caused by insufficient water supply such as occurs in seasons of drought. The immediate cause of the destruction of chlorophyll may indeed be tissue drought, since i t has been shown in Lemna minor, Zea mays, and other plants that decreased water content of the tissues is a characteristic of nitrogen starvation.
Relative Deficiency of Elements Nitrogen hunger may be used to illustrate the fact that the deficiency of one essential element is a matter of relative supply in comparison with others. For example, on the Lebanon, Ill., experiment field in 1939 a 2-12-6 fertilizer was hill-dropped with corn across the variously treated fertility plots a t the rate of 100 pounds an acre (9). On July 4 incipient symptoms of nitrogen starvation were observed in the fertilized portion of the check plot but not on the unfertilized portion. (The check plot had never received lime or fertilizer treatment prior to 1939.) No symptoms showed on either portion of the limestone-sweet clover plot. (This plot had been limed, and sweet clover was plowed down before planting corn.) About 10 days later the symptoms were more
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It is obvious that the soil supply of nitrogen was adequate for the 66-bushel yield of the check plot, and also that this amount was in physiological balance with the phosphate and potash supply, but that this same amount of nitrogen became inadequate when the phosphorus-potassium level was increased by the addition of fertilizer. The 2 per cent of nitrogen in the fertilizer was too small a quantity to be significant. The nitrogen supply where sweet clover had been incorporated with the soil was adequate to balance the high phosphorus-potassium level of the limed sweet clover plot, even when supplemented with more phosphorus and potassium in the hilldropped fertilizer. Phosphorus Deficiency Among the various deficiencies, that of phosphorus is one of the least likely to produce symptoms which can be diagnosed with certainty. The tendency of most crop plants suffering from phosphorus hunger is to grow slowly, mature late, and produce low yields, especially of grain, without exhibiting pronounced symptoms of nutritional unbalance. The late maturity and low grain yields are a reflection of the importance of phosphorus in seed development, as is its normally high accumulation in the seeds a t maturity. I n some species, however, notably in corn and other members of the grass family, a stunted condition of young plants just beyond the seedling stage, together with development of purple coloration in the leaves has been found generally associated with a low level of available phosphorus in the soil. Purple plants and those not showing purple are often found in adjacent hills or even in the same hill. Many qualitative plant tissue tests have shown consistently higher concentrations of phosphate ion in the green plants than in those with purple coloration. I n the spring of 1940 a number of quantitative analyses of the whole plants (tops) gave a narrow range of total phosphorus varying around 0.21 per cent in purple plants, compared to values around 0.32 per cent in green plants from the same or near-by hills. Evidently the soil-supplying power was a t a critical range, and undetermined factors resulted in the differential uptake of phosphorus.
Physiology of Purpling in Corn Plants
Based upon a partial understanding of the biochemistry involved, the following hypothesis is suggested to account for the purpling of corn plants. As previously noted, sugars furnish all the carbon in plant tissues. These sugars undergo chemical modification, and TABLEI. EFFECTOF 2-12-6 FERTILIZER AND SUBSEQUENT the resulting products react with compounds of nitrogen, SODIUM NITRATE ON CORN YIELDS phosphorus, sulfur, and other elements to form the proteins, Yield, Bu. phosphatides, nucleic acids, and many other organic subSoil Treatment per Acre stances found in the living cells. I n normal growth these None, good rotation 66 synthetic processes proceed in orderly fashion so that interNone, good rotation + 2-12-6 hill-dropped at planting mediate products are used up as fast as they are formed; but time 27 None, good rotation + 2-12-6 hill-dropped at planting when one or more stages is retarded or interrupted by untime + NaNOp, mid-July 78 favorable conditions, excessive amounts of intermediate prodCrop residues, limestone, sweet clover, good rotation 124 ucts may accumulate. The presence of these products may Crop residues, limestone, sweet clover, good rotation incite or accelerate other changes and thus start a chain of 2-12-6 hill-dropped 123 events which may have many ramifications. Flavones, mentioned previously, combine with hexose sugars in the leaves, petals, stems, and other parts of plants to form anthocyanins, widespread and more pronounced on the plot on which they and anthocyanidins. These compounds are red to purple were first observed. Soil moisture supply was then adepigments which are responsible for the coloration of the quate. At this time 266 pounds an acre of sodium nitrate blossoms in a wide variety of plants and also for the red, (39.9 pounds nitrogen) were applied and cultivated into the purple, and blue colors in leaves and stems (6, 11). The soil on a portion of this plot; within a few days nitrogen anthocyanidins do not contain the saccharide group. In hunger symptoms had disappeared. On the nonnitrated corn plants the appearance of red to purple colors in the portion they completely overran the plants before shoots were leaves is often but not always accompanied by sugar accumuwell developed, with the result that most of the plants were lation, apparently a result of the above reaction. For exbarren. The yields from these plots are given in Table I.
+
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than in those which are stunted, purple, and phosphorusstarved. Onslow (11, pages 83-104) cites many instances pointing to anthocyanin formation as a result of sugar accumulation; on the other hand, she states (page 82) : “There is without doubt good evidence for believing that anthocyanin is not readily produced where carbon assimilation is most active, and that decreased photosynthesis from any outside cause is favorable to its formation.” I n considering these antithetical viewpoints, it is well to keep in mind that the chloroplasts are found in the deeper lying cells, while the anthocyanin pigments are chiefly formed in the epidermal or immediately subepidermal layers of cells, or the guard cells around the stomata. It is evident that further study is required for the clarification of these questions.
Genetic Aspects of Corn Purpling
FIGVRE 1. LEAFTIPSCOLLAPSE, AND THE EXUDING CONTENTS SEALTHEM TOGETHER A S A RESULTOF CALCIUM STARVATION ample, the reddening of the tip portion of a corn leaf often follows breaking the leaf by a crosswise crease. A possible explanation is that removal of sugars from the distal end of the leaf is retarded, while the sap flow into that portion is sufficient to maintain suitable conditions for photosynthesis and thus provide the sugar concentration required for anthocyanin formation. High sugar content and reddish purple pigmentation in the leaves are especially pronounced in plants approaching maturity where ear development has been prevented. I n young plants, phosphorus deficiency, by failing to provide enough phosphorus for synthesis of phosphorus-containing organic compounds and by retarding protein synthesis by a mechanism to be discussed shortly, would be expected to allow accumulation of the intermediate product, sugar, with consequent purpling. This symptom tends to be intensified by cool weather, especially by a series of cold nights. Low temperatures retard metabolic activities. If the days are warm and sunny, photosynthesis continues a t its normal rate. Protein synthesis is more rapid in the daytime ( I ) , but there is evidence that it also occurs a t night, even in the roots where light is continuously excluded. If protein formation is slowed down by cool nights while photosynthesis continues uninterrupted during the day, conditions are again favorable for sugar accumulation and hence for anthocyanin formation. Purpling has also been found in corn growing in soil not seriously deficient in available phosphorus, but where the root systems were injured by white grubs, corn rootworms, grape colaspis, and other insects. It is conceivable that in such cases the ability of the plant to absorb sufficient phosphorus with its restricted root system might lead t o phosphorus starvation within the plant as in the other cases cited. The grape colaspis in particular feeds by eating the root hairs, and purpling following this injury is particularly prevalent. The sugar data obtained to date do not fully support the theory as stated in regard to the mechariism of purpling in the early post-seedling stage. I n many cases a t this stage sugar concentrations are higher in vigorously growing plants
I n certain inbred lines of corn no trace of purple or red color appeared in the leaves or in other plant parts after phosphorus starvation a t any stage of growth. I n many plant species the ability to form anthocyanins with accompanying coloration is known to be an inherited character, and the genetic aspects of the problem have been studied in some detail for various plant species (11, pages 147-207). This phase of the problem in corn has not been investigated. It has been observed, however, that plants which are incapable of developing purple coloration exhibit chemical behavior (except for anthocyanin formation) similar t o that of purple plants. The leaves turn yellow earlier under phosphorus starvation than do those of plants capable of purpling, and the yellowing and firing symptom becomes more widespread throughout the plant. This yellowing symptom is discussed in the following paragraphs.
Phosphorus Deficiency and Utilization of Nitrogen N7hen corn is grown in controlled sand or gravel cultures with inadequate phosphate supply, purple coloration in the leaves tends to give way, in the fifth to sixth leaf stage, t o yellowing followed by firing. This symptom is practically identical with that of nitrogen hunger. Because of the phosphate deficiency in this situation the plant is apparently unable fully to utilize nitrogen even after it has been taken up. I n these experiments nitrogen was supplied in what is believed to be an adequate amount by a concentration of 140 p. p. m. of N as nitrate in the culture solution. The plants showing symptoms contain very little phosphorus and nitrogen, but the nitrate nitrogen percentage is high, a fact that suggests inability of the plants to convert it to usable forms. The percentage data for 34-day-old plants (Table 11) show that the nitrate nitrogen concentration is twelve times as great (0.46 per cent) in the plants a t the lowest phosphorus-feeding level as in the normal plants grown a t the higher phosphorus-feeding level, where the nitrate nitrogen falls to 0.039 per cent. The nitrogen synthesized into proteins and secondary protein derivatives is only 1.17 times as high in the phosphorus-starved plants as in the others (1.98 compared to 1.69 per cent). These data suggest an impaired ability of the plants to reduce nitrates preparatory to the synthesis of organic forms, as well as impaired ability to bring about subsequent synthesis of more complex compounds. Similar behavior in the tomato is reported by Eckerson (6), who found extreme decrease in the reductase content of phosphorus-starved tomato plants that showed apparent nitrogen starvation symptoms even though high nitrate concentration occurred in the tissues. Physiological nitrogen hunger may thus account for the development of nitrogen hunger symptoms as a result of withholding phosphorus but does not fully account for the shift in symptoms from purple to yellow as the plants grow older. It is evident
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that this chlorosis represents a breakdown of vital cell components, with destruction of chlorophyll and impending death of the cell, whether the causal environmental condition external to the plant is a deficiency of phosphorus, nitrogen, or water or a combination of them.
TABLE11. PHOSPHORUS, NITROGEN,AND SUGAR I N 34-DAYOLD CORNPLANTS GROWN IN GRAVEL CULTURE AT TWO PHOSPHORUS LEVELS (WATER-FREE BASIS) Form of Constituent
Total P sugar Reduoing Tots1 Nitrogen Nitrate Ammonium Amide Residual water-sol. Total water-sol. Water-insol.
Per Cent 30 p.p.m.0
2 p.p.m.a
Mg. per Plant 30 p.p.m.a
2 p.p.m.a
0.118
0.340
-
-
2.14 3.44
12.24 16.26
25.7 41.3
600 796
0.461 0.261 0.082 0.732
0.039 0.066 0,049 0.537
1.91 3.24 2.40 26.31
33.86
-
14.94 __
56.64 -
1.847
33.36
90.50
-
1.536 1.245
0.691 1.156
__
5.53 3.13 0.98 8.78
16.66
18.42
-
Total N 2.781 a Concentration in culture solution.
1.41
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Manganese Toxicity Snider ( l a ) suggested on the basis of chemical studies of field-grown corn that the stunted young purple plants owe their condition to toxicity produced by excess manganese absorption. Most of the phosphorus-deficient soils in the humid region of the Middle West are acid in reaction and contain relatively large amounts of manganese in available forms. The concentrations of manganese in stunted purple corn plants growing on such soils are much higher than in plants not affected, The stunted plants, however, are much smaller, and the high percentage of manganese in the plants seems to be an incident to, rather than a cause of the difficulty. It results from the lack of an excluding mechanism to prevent manganese uptake. Once in the plant the manganese is diluted by the large amount of growth in the normal plants but is not so diluted in those which are stunted. When grown in controlled gravel culture, a toxic excess of manganese produces white chlorosis in irregular patches on the leaves just above the sheath, but no purple color. Purple coloration varies inversely with phosphate ion supplied. After severe purpling has appeared accompanying phosphorus starvation, the addition of a soluble phosphate is followed within a few days by disappearance of the purple color, regardless of whether the manganese concentration is low or high. This is another instance in which a complicated interrelation of different factors interferes with a clean-cut diagnosis.
Potassium Deficiency
FIGURE 2. DIFFERENT HEREDITARY LINESOF CORNREQUIRE WIDELYDIFFERENT AMOUNTS OF CALCIUM FOR NORMAL GROWTH Hybrids containing line B in the parentage do not thrive on highly acid soils.
A review of the functions of potassium in plant growth was given by Hoffer (7). Potassium is of special interest because it does not, so far as is known, enter into permanent organic combinations in growing plants but occurs in solution as the ion. Functions which appear to be associated with the symp toms brought on by deficiency include catalysis of the synthesis and transformations of carbohydrates, the effect on the condition of protoplasmic colloids in the cells (particularly the regulation of water relations), and the prolongation of the time during which the leaves remain green in the autumn. Potassium is the only major essential element which is radioactive, and this property may be related to its importance in photosynthesis. Incipient deficiency is indicated by d i s a p pearance of chlorophyll, producing yellowish stripes alternating with green especially along the margin in parallel-veined plants such as corn, and in yellow or white dots near the margin around the distal end of the leaf in netted veined leaves, such as the legumes. I n larger leaved plants, such as soybeans, potatoes, and tobacco (IO),the chlorotic areas are larger and give a mottled appearance. Necrosis of the spots, which enlarge and merge, follows quickly as the deficiency becomes more severe. This occurrence may be associated with the function of potassium in causing swelling of the cell colloids, retention of water, and resistance to drought, since in potassium starvation drying of the tissues quickly follows chlorosis. The firing, like the initial spotting, is marginal, and in this respect it is in contrast to that of nitrogen hunger. Dead tissue drops out, and the edges of the leaves become ragged in appearance and often curled. Potassium deficiencies are us-
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ually diagnosed fairly accurately in a great variety of plant species by observation of symptoms in the growing plants. In very early stages of the symptom development, potassium and iron deficiency symptoms are often nearly identical. This is particularly true in corn. As the severity increases, however, the potassium-starved leaves promptly fire along the margins, while in iron starvation the entire leaf becomes yellow, first near the base and then progressing outward. No firing occurs for several days, during which the normal green color is restored by supplying iron.
Calcium Deficiency The various species of farm crop plants vary widely in calcium requirements as judged by the composition of the crops. Grain crops are generally low, ranging from 0.15 to 0.5 per cent in the straw or stalks and from 0.01 to 0.02 per cent in the grain. These crops are rarely found to exhibit symptoms traceable to calcium hunger. On the other hand the legumes normally contain from 1.0 to more than 2.5 per cent calcium and with these high requirements might be expected to show deficiency symptoms readily. Acid-sensitive legumes not only have high calcium requirements but also suffer from low p H values; and in soils that are too acid for a given species, they usually succumb in early life to drought or to winterkilling without developing symptoms. Some high-calcium legumes, notably the soybean, are able to secure calcium from acid substrates. Those less tolerant of acidity are unable to absorb even soluble calcium ions in sufficient quantity at low p H values. Crane (4) showed this to be true in the case of red clover. The plants failed to grow satisfactorily in sand cultures below p H 6; and the affected plants were characterized by chlorosis in a pattern of small white dots on the leaves not followed by early necrosis, by emergence of many new leaves a t the crown which failed to enlarge and unfold, and by wilting of petioles of older leaves, followed after a day or two by wilting and death of the leaf. Chemical analyscs (Table 111) revealed failure of the plants to absorb calcium a t low p H values. This is another case of physiological unavailability. The symptoms produced by withholding calcium were identical with those described above, and the plant analysis data were similar as shown in Table 111. This behavior is in harmony with True’s finding (13) many years ago that shortage of calcium disturbed the normal functioning of absorbing surfaces of roots. TABLE111. PLANTWEIQHTSAND CALCIUM UPTAKEBY RED
CLOVER GROWN IN SAND CULTURE
(Ten plants per jar; calcium supplied as CaCIs) 1’. P. &I. of Ca 160 0.16 160
pH 7.0 7.0 5.0
plant Condition Normal Stunted Stunted
Dry Wt. of Plants per Jar, Grams Tops Roots
33 9 3
18
3 1
Ca in plants,
% Tops Roots
1.02 0.40 0.43
0.44 0.42 0.56
Ca in Plants per Jar, Mg. Tops Roots 351 80 48 23 13 6
The importance of calcium in maintaining suitable tone or condition of the cytoplasm in the plant cells is illustrated in hybrid corn studies a t the University of Illinois. Inbred lines with high calcium requirements when grown with deficient calcium suffered collapse and disintegration of the cells in the growing tip; the contents were thus permitted to ooze out and seal the young leaf tips together. Figure 1 illustrates this symptom, which has numerous modifications as to detail. Figure 2 illustrates the wide range in amount of calcium required by two strains of corn. Hybrids obtained by using as one parent the inbred with high calcium requirement have exhibited similar symptoms and have proved unsatisfactory when grown in highly acid soils.
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Minor Elements The number of minor elements necessary for plant growth is not known. They include iron, manganese, boron, zinc, and copper. This field is so new and progress is so rapid that many things learned now may have to be unlearned later. I n certain regions some symptoms of minor element deficiency have been definitely established, such as zinc deficiency in pecans and prunes, and boron deficiency in sugar beets and various truck crops. I n many other cases confusion is evident in the attempts to diagnose symptoms. The difficulties are enhanced by the effects of climatic or other environmental conditions in modifying the symptoms produced. For example, in the northwestern states and western Canada, boron deficiency in alfalfa is definitely identified by a chlorosis known as yellow top (i?), while in hlichigan boron deficiency produces reddening and bronzing of the leaves of alfalfa, alsike, and red clover (5’). The latter symptoms are observed frequently in Illinois, but up to this time i t has not been proved due to boron deficiency. Other physiological aberrations have been observed from time to time, such as the crazy-top corn plants reported by Koehler (8),growing adjacent to foxtail plants showing a similar condition (a modification of floral parts into vegetative tissue). The same symptom in widely different species suggests an external cause. 9 similar symptom in alsike was observed under field conditions, accompanied by the above-described red pigmentation of the leaves. The cause is believed to be nutritional, and boron starvation is suspected. These and other cases of confusion or of uncertainty serve to emphasize the fact that definite knowledge of plant food deficiency symptoms and their meaning must necessarily rest upon a n understanding of the physiological disturbances leading to their development. Summary
Some findings reported in this paper are as follows: 1. The most frequently observed cases of malnutrition are those of deficiencies of one or more essential elements, which may be interpreted as excesses of the elements not deficient. 2. Deficiencies are relative; a sufficient supply of an element under one condition becomes insufficient as other elements become more abundant. 3. Deficiency may be due to: insufficient supply in soil; insufficient solubility rate; physiological unavailability, as in failure of acid-sensitive plants to absorb soluble calcium at low pH; and physiological unavailability within the plant, as failure to reduce absorbed nitrate preparatory t o protein synthesis. 4. There are many kinds of symptoms, roughly grouped into: inhibited growth, no specific symptoms; color symptoms, usually in leaves; necrosis of tissues, usually in leaves; and malformation of different arts of plants. 5 . Plant nutrient ieficiencies produce symptoms indirectly, the symptoms resulting from a series of physiological processes usually out of balance with respect to their various rates. 6. Being an indirect result, a given symptom may follow more than one original cause; e. g., purple-leaved young corn plants may result from phosphorus starvation, from nitrogen starvation, from a series of cold nights with warm sunny days, or from transverse creasing of the leaves-although the immediate cause of the symptom in the leaf is the same in each case. 7. The manner of expression of a deficiency by symptoms is subject to modification by environmental conditions, as temperature, humidity, etc.; as a result the same deficiency in a given crop may produce different symptoms in different geographical regions.
Because of the complicated relations existing between plant maladjustments and plant symptoms, the latter may be considered only as diagnostic aids, rather than as diagnostic methods of certainty. As knowledge of the relation between symptoms and fundamental plant processes increases, their diagnostic value also increases.
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INDUSTRIAL AND ENGINEERING CHEMISTRY
Literature Cited (1) Barton-Wright, E. C., “General Plant Physiolow”, PP. 294-5, Philadelphia, P. Blakiston’s Son h Co., 1938. (2) Besse, R. S.,Oregon Bull. 359 (1938). (3) Cook, R. L., Mich. Agr. Expt. Sta., personal communication. (4) Crane, F. H., Univ. Ill., M.S. thesis, 1926. (5) Eckerson, 8. H., Contrib. BoyceThompson Inst., 3 , 197-217 (1931). (6) Gassner, G., and Strait, W., Angew. Botan., 19,225-45 (1937). (7) Hoffer, G. N.,IND.ENO.CHIM., 30,885-9 (1938). (8) Koehler, B.,Phytopathology, 29, 817-20 (1939).
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(9) Lang, A. L., Dept. Agronomy, Univ. Ill., Mimeographed Leaflet, 1940. (10) McMurtrey, J. E.,U. S. Dept. Agr., Tech. BUZZ. 612 (1938). (11) Onslow, M. W.,“Anthocyanin Pigments of Plants”, 2nd ed., London, Cambridge Univ. Press, 1925. (12) Snider, H. J., Univ. Ill., personal communication. (13) True, R. H., J. Am. SOC.Agron., 13, 91-107 (1921); Science, 55, 1-6 (1922). P R ~ B ~ N before T B D the Division of Fertilizer Chemistry a t the 100th Meeting of tbe Ameriosn Chemiosl Society, Detroit, Mioh.
Chemical Seasoning of Wood Hygroscopic and Antishrink Values of Chemicals EDWARD C. PECK Forest Products Laboratory, Madison, Wis.
O N S I D E R A * B L Ew o r k
chemical, the moisture loss from Of the chemicals and mixtures studied, the the surface layers ceases but has been done a t this ones that showed most promise for use in continues from the interior porlaboratory during recent the chemical seasoning of wood, both from tions which have not become years on the seasoning of wood the standpoint of relative humidity and impregnated. Unless the surwith chemicals. The process antishrink, and of lacking undesirable propfaces are dressed off before the consists in soaking green wood wood is put in service, a chemiin an aqueous solution (usually erties, were urea, invert sugar, and a mixcal of this nature will also cause saturated) of a chemical or mixture of invert sugar and urea. Some of the trouble through condensation of ture of chemicals and in subchemicals studied are too expensive; others moisture from the surrounding sequent air-drying, kiln-drying, possess undesirable properties, such as coratmosphere. or seasoning in service. Somerosiveness or increased flammability. When green wood is immersed times a dry salting method is in a chemical solution, it underused in which the green lumber is Since in commercial practice it is difficult bulk-piled with alternate layers goes certain physical changes. to maintain a solution in any form but a Some of the moisture in the of the chemical. I n the course of saturated one, some chemicals produce too these studies a number of chemiwood will pass into the chemilow a relative humidity with consequent cals and mixtures of chemicals cal solution because of the difdanger of surface checking in the seasoning ferencein vapor pressure between have been tried in an attempt to the green wood and the chemifind the most satisfactory. bath. The safe relative humidity for most cal solution. Some of the A chemical must possess lumber items is probably between 70 and 85 chemical will diffuse into the certain characteristics in order per cent. wood through the water conto be suitable for use in chemitained in the wood, the extent of cal seasoninn. The aaueous this diffusion depending on the nature of the chemical, the solution must cause a considerable reduction in relative vapor duration of the soaking, the available moisture in the wood, pressure or a pronounced antishrink effect when absorbed by wood, or both. It must be cheap and available and readily and the morphological characteristics of the wood. Within soluble in water. It must not be dangerous to handle or corthe penetrated zone, chemical is present in the cell cavities rosive to metals. It may have additional desirable characterand also in the finer wood structure. If the chemical is posiistics, such as decay, insect, or fire resistance. The possession of tively adsorbed within the finer wood structure, swelling some of these properties to an unlimited extent is not always beyond the green dimension takes place; if negatively adsorbed, no swelling takes place, the adsorbed chemical merely wholly beneficial. The solution of a chemical which causes a large reduction in relative humidity is advantageous as far replacing an equivalent volume of water. That which is in as final seasoning is concerned but disadvantageous from the the cell cavities affects the vapor pressure within the cells and acts as a reservoir of chemical for further adsorption standpoint of checking in the chemical bath. When green within the finer wood structure or for further penetration wood is placed in an aqueous solution of a chemical which possesses a low vapor pressure, moisture is lost from the surdeeper into the wood. After soaking in a chemical solution face of the wood because of the vapor pressure difference. a piece of wood possesses an outer zone which contaias a When the surface layers have become impregnated with the gradient of chemical concentration and, therefore, a vapor
C
